The present invention relates to a recording medium in the form of a hologram for recording data based on fringes produced by interference between an object beam from an image representing the data and a reference beam, and an apparatus for and a method of reproducing data recorded in the recording medium.
There are known in the art holographic recording mediums for recording various data based on fringes produced by interference between an object beam and a reference beam. It is also known in the art that the holographic recording mediums can have a high recording density for large storage capacity. The holographic recording mediums are considered to be useful as large-capacity storage mediums for storing computer data and AV (Audio-Video) contents data such as audio and video data, for example.
For recording data in a holographic recording medium, the data is converted into image data as two-dimensional page data. The data is displayed on a liquid crystal panel or the like, and a light beam that has passed through the liquid crystal panel, i.e., an object beam representing an image of the two-dimensional page data, is applied to the holographic recording medium. In addition, a reference beam is applied at a certain angle to the holographic recording medium. The object beam and the reference beam interfere with each other, producing fringes that can be recorded as a single element hologram. Therefore, a single element hologram is a recorded form of one two-dimensional page data.
Japanese patent laid-open No. 2005-32308 discloses an optical information recording process for achieving a large storage capacity on a holographic recording medium according to shift multiplexing and angle multiplexing. According to shift multiplexing, a colinear optical system is used to convert a reference beam into a convergent (or divergent) beam for recording a succession of overlapping element holograms on the holographic recording medium for an increased recording density. According to angle multiplexing, the angle of a reference beam is changed to record a number of overlapping element holograms at the same position on the holographic recording medium for an increased recording density.